Our games need support for handling objects that collide. Balls bouncing off
paddles, laser beams hitting aliens, or our favorite character collecting a
coin. All these examples require collision detection.

The Arcade library has support for sprites. A sprite is a two-dimensional
image that is part of the larger graphical scene. Typically a sprite will
be some kind of object in the scene that will be interacted with like a car,
frog, or little plumber guy.

Originally, video game consoles had built-in hardware support for sprites.
Now this specialized hardware support is no longer needed, but we still use
the term “sprite.” The history of sprites is interesting, if you want to
read up more about it.

.bmp - Bitmap. This is an uncompressed image that normally uses three bytes to represent each dot in the image.
These files can be very large. Because there are so many better options, this format is not used often. It is,
however, the simplest format to use.

.png - Great patent-free format for line art and clip art. Not great for photos. Can’t hold animations.

.gif - Great format for line art and clip art. Has had issues with patents (now expired). Can do animations.

.jpg - Great file format for photos. Terrible for clip-art. Don’t use for sprites.

.svg - File format for storing line-art images that can scale to any resolution. Not compatible with the
“arcade” library.

If you use Google’s advanced image search you can find images that are “icon” sized, and either png or gif file
format.

There’s also a great source for images from kenney.nl. He has a lot of free and cheap game image assets.
That’s where the following images come from that we will use in our examples:

Where should you save them? If you load your sprite with the code
below, the computer will look for the character.png image in the same
directory as your Python file. Save the image anywhere else, and it won’t
be found.

Let’s step through an example program that uses sprites. This example shows how
to create a screen of sprites that are coins, and collect them using a sprite
that is a character image
controlled by the mouse as shown in the figure below. The program keeps “score”
on how many coins have been collected. The code for this example may be found at:

The first few lines of our program start off like other games we’ve done. We
import a couple libraries. Set a couple constants for the size of the screen,
and a couple new constants that we will use to scale our graphics.

The example below should have nothing new, it just creates a window and sets a
background color. We’ll add in the new stuff soon.

player_list: When working with sprites, we normally put them into
lists. Other game engines might call these sprite groups, or sprite layers.
Our game will have one list for the player, and one list for the coins.
Even if there is only one sprite, we should still put it in a list because
there is a lot of code in SpriteList to optimize drawing.

coin_list: This is a list of all the coins. We will be checking if the
player touches any sprite in this list.

player_sprite: This points to our player’s sprite. It is the sprite
we will move.

score: This keeps track of our score.

We use a command built into the parent Window class called
set_mouse_visible to make the mouse not visible. Finally we set the
background color.

Next up, we will create a setup method. This will create our sprites and get
our game set up. We do this in a different method than __init__ so that
if we ever want to restart the game, we can just call setup again.

The setup method is not called automatically.
Therefore in the example below, note we have added the
code that calls the setup function near the end: window.setup().

""" Sprite Sample Program """importrandomimportarcade# --- Constants ---SPRITE_SCALING_PLAYER=0.5SPRITE_SCALING_COIN=0.2COIN_COUNT=50SCREEN_WIDTH=800SCREEN_HEIGHT=600classMyGame(arcade.Window):""" Our custom Window Class"""def__init__(self):""" Initializer """# Call the parent class initializersuper().__init__(SCREEN_WIDTH,SCREEN_HEIGHT,"Sprite Example")# Variables that will hold sprite listsself.player_list=Noneself.coin_list=None# Set up the player infoself.player_sprite=Noneself.score=0# Don't show the mouse cursorself.set_mouse_visible(False)arcade.set_background_color(arcade.color.AMAZON)defsetup(self):""" Set up the game and initialize the variables. """# Sprite listsself.player_list=arcade.SpriteList()self.coin_list=arcade.SpriteList()# Scoreself.score=0# Set up the player# Character image from kenney.nlself.player_sprite=arcade.Sprite("character.png",SPRITE_SCALING_PLAYER)self.player_sprite.center_x=50self.player_sprite.center_y=50self.player_list.append(self.player_sprite)defon_draw(self):arcade.start_render()# Draw the sprite lists here. Typically sprites are divided into# different groups. Other game engines might call these "sprite layers"# or "sprite groups." Sprites that don't move should be drawn in their# own group for the best performance, as Arcade can tell the graphics# card to just redraw them at the same spot.# Try to avoid drawing sprites on their own, use a SpriteList# because there are many performance improvements in that code.self.coin_list.draw()self.player_list.draw()defmain():""" Main method """window=MyGame()window.setup()arcade.run()if__name__=="__main__":main()

How does the code above work?

First, we need some lists to hold our sprites. We could do use a list like
this:

coin_list=[]

But wait! coin_list is an instance variable that’s part of our class.
we need to prepend it with self..

self.coin_list=[]

However, the Arcade library has a class especially for handling sprite lists.
This class is called SpriteList.
For more information, check out the SpriteList documentation.
So instead of creating an empty list with
[], we will create a new instance of the SpriteList class:

self.coin_list=SpriteList()

Except that doesn’t work. Why? SpriteList is in the Arcade library. We
need to prepend any reference to things in the Arcade library with arcade
of course, so now we have:

self.coin_list=arcade.SpriteList()

We need a separate list for just coins. This list won’t have the player. We also
need to reset our score to 0.

self.coin_list=arcade.SpriteList()self.score=0

Now we need to create our sprites. The name of the class that represents sprites
is called Sprite. You can read more about it by looking at the Sprite
documentation.
The Sprite constructor takes two parameters. A path to the image we will be
using, and how big to scale it.

For class, please source the image right before you load it. If you drew your own image, please note that as well.

# Character image from kenney.nlself.player_sprite=arcade.Sprite("character.png",SPRITE_SCALING_PLAYER)

How do we draw all our sprites? Really easy. Just call the draw method that
exists for us in the SpriteList class. We just need to do this for each of
our sprite lists.

defon_draw(self):arcade.start_render()# Draw all the sprite lists.self.coin_list.draw()self.player_list.draw()

Wait. We don’t have many sprites. There are no coins, and we have just the player.
Let’s add a for loop to our program and create a bunch of coins:

""" Sprite Sample Program """importrandomimportarcade# --- Constants ---SPRITE_SCALING_PLAYER=0.5SPRITE_SCALING_COIN=0.2COIN_COUNT=50SCREEN_WIDTH=800SCREEN_HEIGHT=600classMyGame(arcade.Window):""" Our custom Window Class"""def__init__(self):""" Initializer """# Call the parent class initializersuper().__init__(SCREEN_WIDTH,SCREEN_HEIGHT,"Sprite Example")# Variables that will hold sprite listsself.coin_list=Noneself.player_list=None# Set up the player infoself.player_sprite=Noneself.score=0# Don't show the mouse cursorself.set_mouse_visible(False)arcade.set_background_color(arcade.color.AMAZON)defsetup(self):""" Set up the game and initialize the variables. """# Sprite listsself.player_list=arcade.SpriteList()self.coin_list=arcade.SpriteList()# Scoreself.score=0# Set up the player# Character image from kenney.nlself.player_sprite=arcade.Sprite("character.png",SPRITE_SCALING_PLAYER)self.player_sprite.center_x=50self.player_sprite.center_y=50self.player_list.append(self.player_sprite)# Create the coinsforiinrange(COIN_COUNT):# Create the coin instance# Coin image from kenney.nlcoin=arcade.Sprite("coin_01.png",SPRITE_SCALING_COIN)# Position the coincoin.center_x=random.randrange(SCREEN_WIDTH)coin.center_y=random.randrange(SCREEN_HEIGHT)# Add the coin to the listsself.coin_list.append(coin)defon_draw(self):""" Draw everything """arcade.start_render()# Draw the sprite lists here. Typically sprites are divided into# different groups. Other game engines might call these "sprite layers"# or "sprite groups." Sprites that don't move should be drawn in their# own group for the best performance, as Arcade can tell the graphics# card to just redraw them at the same spot.# Try to avoid drawing sprites on their own, and not in a layer.# There are many performance improvements to drawing in a layer.self.coin_list.draw()self.player_list.draw()defmain():""" Main method """window=MyGame()window.setup()arcade.run()if__name__=="__main__":main()

""" Sprite Sample Program """importrandomimportarcade# --- Constants ---SPRITE_SCALING_PLAYER=0.5SPRITE_SCALING_COIN=0.2COIN_COUNT=50SCREEN_WIDTH=800SCREEN_HEIGHT=600classMyGame(arcade.Window):""" Our custom Window Class"""def__init__(self):""" Initializer """# Call the parent class initializersuper().__init__(SCREEN_WIDTH,SCREEN_HEIGHT,"Sprite Example")# Variables that will hold sprite listsself.player_list=Noneself.coin_list=None# Set up the player infoself.player_sprite=Noneself.score=0# Don't show the mouse cursorself.set_mouse_visible(False)arcade.set_background_color(arcade.color.AMAZON)defsetup(self):""" Set up the game and initialize the variables. """# Sprite listsself.player_list=arcade.SpriteList()self.coin_list=arcade.SpriteList()# Scoreself.score=0# Set up the player# Character image from kenney.nlself.player_sprite=arcade.Sprite("character.png",SPRITE_SCALING_PLAYER)self.player_sprite.center_x=50self.player_sprite.center_y=50self.player_list.append(self.player_sprite)# Create the coinsforiinrange(COIN_COUNT):# Create the coin instance# Coin image from kenney.nlcoin=arcade.Sprite("coin_01.png",SPRITE_SCALING_COIN)# Position the coincoin.center_x=random.randrange(SCREEN_WIDTH)coin.center_y=random.randrange(SCREEN_HEIGHT)# Add the coin to the listsself.coin_list.append(coin)defon_draw(self):""" Draw everything """arcade.start_render()self.coin_list.draw()self.player_list.draw()# Put the text on the screen.output=f"Score: {self.score}"arcade.draw_text(output,10,20,arcade.color.WHITE,14)defon_mouse_motion(self,x,y,dx,dy):""" Handle Mouse Motion """# Move the center of the player sprite to match the mouse x, yself.player_sprite.center_x=xself.player_sprite.center_y=ydefmain():""" Main method """window=MyGame()window.setup()arcade.run()if__name__=="__main__":main()

Each sprite has its own update method. This allows sprites to move and
animate its images. Right now, our sprite does not have this method. But we
will soon. Rather than call the update method of each sprite we have,
there is an update method in each sprite list that will call update
on each sprite in the list. Therefore, just calling update with our
coin_list will cause all coin sprites to update.

self.coin_list.update()

How do we detect what coins are touching the player? We call the
check_for_collision_with_list method. Pass it in our player sprite,
along with a list of all the coins. That function will return a list of
all colliding sprites. If no sprites collide, the list will be empty.

# Generate a list of all sprites that collided with the player.coins_hit_list=arcade.check_for_collision_with_list(self.player_sprite,self.coin_list)

What do we do with this hit_list we get back? We loop through it. We add one
to the score for each sprite hit.

We also need to get rid of the sprite. The sprite class has a method called
kill. This method will remove the sprite from existence.

# Loop through each colliding sprite, remove it, and add to the score.forcoinincoins_hit_list:coin.remove_from_sprite_lists()self.score+=1

""" Sprite Sample Program """importrandomimportarcade# --- Constants ---SPRITE_SCALING_PLAYER=0.5SPRITE_SCALING_COIN=0.2COIN_COUNT=50SCREEN_WIDTH=800SCREEN_HEIGHT=600classMyGame(arcade.Window):""" Our custom Window Class"""def__init__(self):""" Initializer """# Call the parent class initializersuper().__init__(SCREEN_WIDTH,SCREEN_HEIGHT,"Sprite Example")# Variables that will hold sprite listsself.player_list=Noneself.coin_list=None# Set up the player infoself.player_sprite=Noneself.score=0# Don't show the mouse cursorself.set_mouse_visible(False)arcade.set_background_color(arcade.color.AMAZON)defsetup(self):""" Set up the game and initialize the variables. """# Sprite listsself.player_list=arcade.SpriteList()self.coin_list=arcade.SpriteList()# Scoreself.score=0# Set up the player# Character image from kenney.nlself.player_sprite=arcade.Sprite("character.png",SPRITE_SCALING_PLAYER)self.player_sprite.center_x=50self.player_sprite.center_y=50self.player_list.append(self.player_sprite)# Create the coinsforiinrange(COIN_COUNT):# Create the coin instance# Coin image from kenney.nlcoin=arcade.Sprite("coin_01.png",SPRITE_SCALING_COIN)# Position the coincoin.center_x=random.randrange(SCREEN_WIDTH)coin.center_y=random.randrange(SCREEN_HEIGHT)# Add the coin to the listsself.coin_list.append(coin)defon_draw(self):""" Draw everything """arcade.start_render()self.coin_list.draw()self.player_list.draw()# Put the text on the screen.output=f"Score: {self.score}"arcade.draw_text(output,10,20,arcade.color.WHITE,14)defon_mouse_motion(self,x,y,dx,dy):""" Handle Mouse Motion """# Move the center of the player sprite to match the mouse x, yself.player_sprite.center_x=xself.player_sprite.center_y=ydefupdate(self,delta_time):""" Movement and game logic """# Call update on all sprites (The sprites don't do much in this# example though.)self.coin_list.update()# Generate a list of all sprites that collided with the player.coins_hit_list=arcade.check_for_collision_with_list(self.player_sprite,self.coin_list)# Loop through each colliding sprite, remove it, and add to the score.forcoinincoins_hit_list:coin.remove_from_sprite_lists()self.score+=1defmain():""" Main method """window=MyGame()window.setup()arcade.run()if__name__=="__main__":main()